Microelectronic devices, such as semiconductor devices and field emission displays, are generally fabricated on and/or in microfeature workpieces using several different types of machines (“tools”). Many such processing machines have a single processing station that performs one or more procedures on the workpieces. Other processing machines have a plurality of processing stations that perform a series of different procedures on individual workpieces or batches of workpieces. In a typical fabrication process, one or more layers of conductive materials are formed on the workpieces during deposition stages. The workpieces are then typically subject to etching and/or polishing procedures (i.e., planarization) to remove a portion of the deposited conductive layers for forming electrically isolated contacts and/or conductive lines.
Plating tools that plate metals or other materials on the workpieces are becoming an increasingly useful type of processing machine. Electroplating and electroless plating techniques can be used to deposit nickel, copper, solder, permalloy, gold, silver, platinum and other metals onto workpieces for forming blanket layers or patterned layers. A typical metal plating process involves depositing a seed layer onto the surface of the workpiece using chemical vapor deposition (CVD), physical vapor deposition (PVD), or other suitable methods. After forming the seed layer, a blanket layer or pattern layer of metal may be deposited on the workpiece by an appropriate electroplating or electroless processing technique. In either process, the workpiece may then be cleaned, etched and/or annealed in subsequent procedures before transferring the workpiece to another processing machine.
One potential drawback with the foregoing techniques is that depositing the seed layer can be a time consuming process that typically requires a specialized process station. One approach to addressing this problem is to reduce the thickness of the seed layer so as to reduce the time required to deposit the seed layer. One potential drawback with this solution is that it can be difficult to uniformly electrolytically plate a blanket layer on a very thin seed layer. For example, the current density may vary over a thin seed layer, leading to nonuniformities in the applied blanket layer. In one particular example, the current density may be significantly higher near the junctions between the seed layer and a contact assembly (which applies an electrical charge to the seed layer), than it is at points distant from these junctions. This effect is referred to in the industry as the “terminal effect.” The terminal effect can result in electroplated layers that (a) are not uniformly thick and/or (b) contain voids and/or (c) non-uniformly incorporate impurities or defects. These characteristics tend to reduce the effectiveness and/or reliability of the devices formed from the microfeature workpiece.